Greer has difficulty trusting people who are not part of the military, such as Dr. Nicholas Rush. Surprisingly, the only civilian that Greer appears to trust to any degree is Eli Wallace, this is likely either because Colonel Young trusts Eli, or because Greer perceives Eli's innocence. At first glance it seems he has anger issues, but he cares about those aboard the ship. Although he is clever and calm during a struggle, he believes that he can only count on other soldiers during combat and has a hard time trusting the non-Starfleet/Marine personnel. Greer prioritizes survival over comfort, dismissing the awful taste of an alien sweet potato for the simple reason that it will keep them alive. His sense of humor is unusual but good at mediating conflicts when they arise.